class Dog():
    """ 一次模拟小狗的简单尝试 """

    def __init__(self, name, age):
        """ 初始化属性name和age """
        self.name = name
        self.age = age

    def sit(self):
        """ 模拟小狗被命令时蹲下 """
        print(self.name.title() + " is now sitting.")

    def roll_over(self):
        """ 模拟小狗被命令时打滚 """
        print(self.name.title() + " rolled over!")


my_dog = Dog('willie', 6)

print("My dog's name is " + my_dog.name.title() + ".")
print("My dog is " + str(my_dog.age) + " years old.")
my_dog.sit()
my_dog.roll_over()

your_dog = Dog('luck', 3)
print("\nYour dog's name is " + your_dog.name.title() + ".")
print("Your dog is " + str(your_dog.age) + " years old.")
your_dog.sit()
your_dog.roll_over()
